Powershell XML cannot count to 1

OK, I have an xml file with following contents:

<?xml version="1.0" ?>
<Objects>
  <Object Name="Name01">
    <Number>123465</Number>
    <Pictures FolderName="D:\Temp\Pictures01">
      <Picture Name="0001.jpg"/>
      <Picture Name="0002.jpg"/>
      <Picture Name="0003.jpg"/>
      <Picture Name="0004.jpg"/>
    </Pictures>
  </Object>
  <Object Name="Name02">
    <Number>123465</Number>
    <Pictures FolderName="D:\Temp\Pictures01">
      <Picture Name="0005.jpg"/>
      <Picture Name="0006.jpg"/>
    </Pictures>
  </Object>
  <Object Name="Name03">
    <Number>123465</Number>
    <Pictures FolderName="D:\Temp\Pictures01">
      <Picture Name="0013.jpg"/>
    </Pictures>
  </Object>
  <Object Name="Name04">
    <Number>123465</Number>
  </Object>
</Objects>

I read it in using this statement:
$MyXMLFile = [xml] (Get-Content -Path ".\MyXMLFile.xml")

I get the first "Object"
$CurrentObject = $MyXMLFile.Objects.Object | Select-Object -First 1
Then I see how many "Pictures" it points to:
$CurrentObject.Pictures.Picture.Count
This gives me 4

I get the next object
$CurrentObject = $MyXMLFile.Objects.Object | Select-Object -First 1 -Skip 1
$CurrentObject.Pictures.Picture.Count
This gives me 2

Now the surprise:
$CurrentObject = $MyXMLFile.Objects.Object | Select-Object -First 1 -Skip 2
$CurrentObject.Pictures.Picture.Count
This gives me $Null, apparently it doesn't even have a Count member even though its a System.Xml.XmlElement like the previous two.

The next step is logical again
$CurrentObject = $MyXMLFile.Objects.Object | Select-Object -First 1 -Skip 3
$CurrentObject.Pictures.Picture.Count
This gives me 0

Can anyone explain the $Null?